This invention relates to a wastewater treatment process, and particularly a process for treating nitrogen-deficient wastewater.
Aerobic biological processes are one of the mainstays for treatment of industrial wastewater containing organic contaminants. In such processes, bacteria consume the wastewater contaminants and are encouraged to proliferate in reactor systems under intensive aeration. These bacteria both consume the contaminants and create a sludge which ultimately must be disposed of at the end of the treatment process. Such contaminated sludge is difficult to de-water and dispose of within the local regulations governing effluent discharge. Thus, high bacterial growth, whilst it may increase contaminant consumption, also increases sludge production and, therefore, disposal costs.
A variety of process conformations, such as activated sludge moving bed biofilm reactors, aerated lagoons and aeration stabilisation basins, are used for industrial scale biological treatment. The aerated lagoons and stabilisation basins are low rate biological processing systems, whilst activated sludge and variant system""s, and moving bed biofilm reactors are high rate biological processing systems.
For high rate treatment systems such as activated sludge, a biochemical oxygen demand (BOD):nitrogen ratio of 100:5 in the incoming wastewater is generally considered to be sufficient to supply the nitrogen requirements for bacterial growth. Typical BOD:nitrogen ratios for other industrial, non-nitrogen-deficient wastewaters and municipal sewage are given below (Couper and Maclennan, (1997) xe2x80x9cProcess design aspects of activated sludge for industrial wastewater treatmentxe2x80x9d, Proceedings of the 1997 Annual Conference of the New Zealand Water and Wastes Association, pp 74-81; and Metcalf and Eddy (1979) xe2x80x9cWastewater engineering treatment disposal reusexe2x80x9d, Tata McGraw-Hill, New Delhi).
Pulp and paper mill wastewaters are typically deficient in nutrient nitrogen, which is essential to support the bacterial growth required for biological treatment of wastewaters. Conventionally, activated sludge processes used in the pulp and paper industry have been operated with the addition of nitrogen to the system, typically in the form of urea. This can be a considerable operating expense. Moreover, it can result in excessive levels of ammoniacal nitrogen in the discharge wastewater, which can become a very significant problem in the receiving water environment. A similar problem arises with a range of industrial wastewaters which are nitrogen-deficient.
A nitrogen-deficient wastewater is herein defined as a wastewater for which, due to lack of available nitrogen in the wastewater, an additional nitrogen source is required for the biological consumption of the biodegradable organic material present.
Thus, it is an object of the present invention to provide a wastewater treatment process, particularly for nitrogen-deficient wastewater, which overcomes or at least reduces the above-mentioned problems, or which at least provides the public with a useful alternative.
Other objects of the present invention may become apparent from the following description, which is given by way of example only.
According to one aspect of the present invention there is provided a biological wastewater treatment process wherein a controlled environment is provided for the encouragement of nitrogen-fixing microorganisms, said controlled environment provided through the supply of a nitrogen-deficient feed and maintenance of a substantialy stable dissolved oxygen level in said controlled environment.
Preferably the BOD:nitrogen ratio in the nitrogen-deficient feed may be no lower than 100:5, more preferably no lower than 100:2, and most preferably greater than 100:1.
Preferably, the process may further comprise monitoring the dissolved oxygen level in the controlled environment.
Preferably, the dissolved oxygen level may be controlled at a level which optimises organic matter removal in relation to biomass yield or settleability.
In one preferred form the process of the invention may further include transfer of the substantially nitrogen-deficient feed from a first tank or zone having a first substantially stable dissolved oxygen level to a second tank or zone having a second substantially stable dissolved oxygen level.
In one preferred process of the present invention, the substantially nitrogen-deficient feed may comprise industrial wastewater from an industry producing substantialy nitrogen-deficient wastewater.
Preferably, said process may further comprise seeding said controlled environment with nitrogen-fixing bacteria.
Preferably a biological wastewater treatment process of the invention may produce a low soluble nitrogen processed wastewater, without nitrogen supplementation.
According to a further aspect of the present invention, there is provided biological wastewater treatment apparatus including a controlled environment including nitrogen-fixing organism, means for maintaining a substantially stable dissolved oxygen level in the controlled environment, means for supplying a nitrogen-deficient wastewater to the controlled environment, and an outflow from the controlled environment.
Preferably, the controlled environment may include at least two tanks or zones, at least one having a lower substantially stable dissolved oxygen level and at least another having a higher substantially stable dissolved oxygen level.
According to a further aspect of the invention there is provided a biological wastewater treatment apparatus including:
a first controlled environment including nitrogen-fixing organisms and means for maintaining a substantially stable dissolved oxygen level,
means for supplying a nitrogen-deficient wastewater to the first controlled environment,
a second controlled environment including non-nitrogen-fixing organisms,
means for transferring a partially-processed wastewater from the first controlled environment to the second controlled environment, and
an outflow for processed wastewater from the second controlled environment.
Preferably, the process end apparatus of the invention involves a high rate biological processing system.
According to a further aspect of the present invention there is provided the biomass derived from a biological wastewater treatment process as herein described.
Other aspects of the present invention may become apparent from the following description, which is given by way of example only.